Such a light may be a "cheap" light, in the sense that a "cheap" light is a signal light which, in conventional manner, is not provided with a reflector, and which includes a light source such as a filament lamp together with a spherical Fresnel lens or the like which is essentially flat and is placed in front of the source and is focused thereon. Diffusion beads may also be provided downstream from the lens in order to make the beam more uniform.
This technique provides a relatively concentrated light beam suitable for satisfying most of the photometric requirements for motor vehicle signal lamps in a relatively cheap manner.
However, such a light suffers from the drawback whereby only a small portion of the light flux emitted by the lamp is recovered for the purpose of constituting the beam. More precisely, the only useful light is the light which is emitted in the solid angle occupied by the Fresnel lens as seen from the source, with the remainder of the light flux being irremediably lost.
In general, the light flux recovered with such a prior light constitutes about 15% to 25% of the total emitted light flux, depending on the size of the lens and on its distance from the source.
Further, the area illuminated by such a light suffers from a marked lack of uniformity in that those zones of the lens which are furthest from the source receive a much smaller quantity of light per unit area than do zones which are close to the source, i.e. which are close to the optical axis of the light. As a result, the luminance falls off progressively towards the edges of the illuminated area in a way which is clearly visible.
The object of the present invention is to mitigate these drawbacks of the prior art and to provide a signal light which, while remaining cheap to manufacture, nevertheless provides improved recovery of the total flux available from the source together with greater uniformity of the resulting illuminated area.